Radioactive leucine (H3) will be injected into vitreous bodies of mature and developing normal dogs. Animals will be killed at various times after injection, thin sections made of retinal tissue and these prepared for radioautography. Rod disc turnover interval should thus be determined. Retinal dystrophic irish setter dogs will be similarly prepared and rod disc turnover time compared with information gained from the normal animals. Purpose of study is to gain rod disc turnover rate in normal dogs. This information should be useful in further evaluating the retinal dystrophy found in Irish setters.